The present invention relates to a suction air filter for internal combustion engines of a hand-operated working tool like a cut-off tool or the like with a housing being provided with an inlet opening for intake air and an outlet opening for clean air which is supplied as combustion air to the suction channel of the internal combustion engine and being provided within the housing with a filter body between the inlet opening and the outlet opening.
Such a suction air filter for a hand-operated working tool is known from U.S. Pat. No. 5,073,307. A carburetor sucks clean air into a suction channel for producing the fuel/air mixture whereby the supplied air is cleaned from dirt particles of the intake air in an air filter located upstream of the carburetor. The filter body of the air filter is constructed as a ring filter. The intake air enters the filter from the outer mantle surface. Dirt particles are filtered by the filter from the contaminated intake air. A radially inwardly directed air flow is created because of the pressure difference between outer and inner side of the ring filter. The cleaned air within the interior space of the ring filter is supplied to the suction channel of the carburetor via an outlet opening of the air filter. Such a ring filter must provide a high filter action, particularly if installed in working tools like cut-off tools, in order to be able to effectively filter the dirt particles, which are created during operation of the working tool, from the intake air and thus to prevent a contamination of the carburetor and an increased wear of the internal combustion engine. The application of very fine-pored filters, however, only provides a very short service life due to the rapid clogging of the filter pores since the filter action decreases considerably and, moreover, the pressure within the suction channel decreases considerably so that a loss of performance is to be expected.
On the other hand, the application of large-pored filters carries the risk that fine and finest dirt particles pass through the ring filter unimpededly and deposit within the interior of the carburetor and of the combustion engine, possibly leading to permanent damage.
Moreover, when removing the air filter for maintenance and cleaning purposes, there is a risk that small and large dirt particles can enter the exposed suction channel of the carburetor.
It is, therefore, an object of the invention to keep the pressure drop within the air filter as low as possible during a longer service life of the working tool and to increase the service life of the air filter.